Geochemical exploration method



dice

Patented July 12, i. 55

GEOCHEMICAL ExrLoRA'rioN METHOD William B. Huckabay, Dallas, Tex, assignor, by mesne assignments, to Socony-Vacuum (Bil Company, Incorporated, New York, N. Y., a corporation of Texas No Drawing. Application Eeptember 8, 1953,

Serial No. 379,071

12 Claims. (Cl. 23-230) This invention relates to geochemical exploration and relates more particularly to a geochemical exploration method for petroleum hydrocarbon reservoirs.

In the location of underground petroleum hydrocarbon reservoirs, extensive use has been made of geochemical methods. These methods are based on the theory that hydrocarbons migrate upwardly from the underground reservoirs and their presence in the surface or near surface zones or in the strata intermediate to the near surface zones, as an anomaly, i. e., in quantity greater than the back round quantity due to causes other than the presence of a petroleum reservoir, are indicative of the location of an underlying petroleum reservoir. Thus, as a prospecting method or a Well logging method, samples of earth material have been collected and analyzed for parafiin hydrocarbons having two or more carbon atoms, anomalies of which are regarded as diagnostic of an underground petroleum reservoir. It has been observed, however, that parafiin hydrocarbon anomalies may be present in areas wherein petroleum reservoirs are absent and anomalies may be absent or ill defined in areas wherein petroleum reservoirs are present.

it is KZIOWQ that the amount of any given com-pound or compounds, such as hydrocarbons, that may be retained or absorbed by a porous material, such as earth, depends, among other things, on the amount of the compound or compounds available for absorption but also on the type and characteristics of the porous material. Accordingly, variations in amount of hydrocarbons in earth samples as determined by analysis of the samples may not be governed by the amount of petroleum derived hydrocarbons available for absorption, which would be the true anomaly indicative of the presence of the petroleum reservoir, but may be governed by the absorption characteristics of the earth at the points where the samples are taken. hydrocarbon anomalies in areas where petroleum reservoirs are absent and the absence of anomalies in areas where petroleum reservoirs are present are due, in many instances, to variations in the ability of earth to retain or absorb paraffin hydrocarbons.

it is an object of this invention to provide a geochemi- C31 exploration method. it is another object of this invention to provide a correction in geochemical exploration methods for variations in ability of the earth to retain materials diagnostic of petroleum reservoirs. It is another obiect of this invention to improve the reliability of diagnostic parafiin hydrocarbon anomalies. These and other objects of the invention will become apparent from the following description thereof.

in accordance with my invention, earth samples are analyzed for paratiin hydrocarbon and for lipids, and the ratio of the amount of paraffin hydrocarbon to the amount of lipids is regarded as diagnostic of the proximity of a petroleum reservoir.

Lipids are a group of naturally occurring compounds of animal and vegetable origin and are generally regarded as substances having the following characteristics: (1)

I have discovered that the presence of paraffin insolubility in Water and solubility in the fat solvents, such as ether, chloroform, and benzene; (2) relationship to the fatty acids as esters, either actual or potential; and (3) utilization by living organisms. They may be classified as simple liquids, compound lipids, and derived lipids. The simple lipids are esters of fatty acids with various alcohols and include fats which are esters of the fatty acids with glycerol and which are solid at room temperature, oils which are esters of the fatty acids with glycerol and which are liquid at room temperature, and Waxes which are esters of the fatty acids with alcohols other than glycerol, the alcohols commonly being monatomic. The compound lipids are esters of fatty acid-containing groups in addition to an alcohol and fatty acid and include phospholipids which are substituted fats containing phosphoric acid and nitrogen such as lecithin, cephalin, and sphingomyelin, cerebrosides which are compounds of the fatty acids containing both a carbohydrate and a nitrogen base but containing neither glycerol nor phosphoric acid, such as phrenosin, kerasin, and nervon, and amino-lipids and sulfolipids. The derived lipids are substances derived from the simple lipids and the compound lipids by hydrolysis and include the fatty acids, sterols, alcohols, and nitrogen bases.

Many of the lipids are widely distributed in the earth not only in the surface and near surface zones but also in subterranean sedimentary zones. Their presence in the earth arises from the presence of animal and vegetable debris in the earth such as leaves, twigs, branches, and other parts of trees and shrubs, grass, insects, animals, bacteria, etc., which debris may be of recent origin and of comparatively ancient origin. While the concentration of these lipids in the earth, taking into consideration the variations in the capability of the earth to retain or absorb these compounds and the availability of animal and vebetable debris, is not uniform, the variations in the concentration over wide areas are quite small. Accordingly, any marked variations in the lipid concentration of the earth in any particular area is apt to be due to the absorption ability of the earth rather than due to the amount of the lipids which may have been available for absorption. Thus, the lipid concentration in the earth becomes a measure of the absorption ability of the earth material. in accordance with my invention, by analyzing earth samples for paralfin hydrocarbons and for lipids and employing the ratio of the amount of parafiin hydrocarbon to the amount of the lipids as a parameter for the determination of anomalies diagnostic of petroleum reservoirs, errors arising from the variations in the absorption characteristics of the earth are eliminated and the presence or absence of anomalies related to the paraffin hydrocarbon content of the earth samples become more dependable as indicating the presence or absence of petroleum reservoirs.

The parafiin hydrocarbons contained in an earth sample as a result of migration from a petroleum reservoir constitute methane and those paraffin hydrocarbons having a greater number of carbon atoms, for example up to sixteen carbon atoms or more. Thus, the ratio of the amount of any of these paraffin hydrocarbons to the amount of lipids in the earth sample as an anomaly may be regarded as diagnostic of the proximity of a petroleum reservoir. Accordingly, analysis of the earth samples may be made for all parafiin hydrocarbons, single paraffin hydrocarbons, or groups of paraflin hydrocarbons, provided, of course, that analysis of each earth sample in the exploration Zone is made for the same paraffin hydrocarbon or groups of parafiin hydrocarbons, or, to attain a similar result, the same analytical procedure for paraffin hydrocarbons is employed for each earth sample. While methane may be present in earth samples as a result of migration from a petroleum reservoir, it may also be present as a result of other causes such as vegetative decomposition, and, for this reason, methane should 'be excluded from the paraflin hydrocarbons for which analysis is made if its presence could be due to causes other than migration from a petroleum reservoir.

7 It is not necessary to determine the ratio of the particular paraffin hydrocarbon or hydrocarbons selected to all the lipids contained in the earth samples, although it is preferred to do so. It is only necessary to determine.

the ratio of the parafiin hydrocarbon or hydrocarbons selected'to some of the lipids whose concentration will be representative of the absorption abilities of the earth samples. Thus, analysis of the earth samples may be made for all or only a portion of the lipids, provided here again, of course, that analysis of each earth sample in the exploration zone is made for the same lipid portion, or, to attain a similar result, the same analytical procedure for lipids is employed for each earth sample.

The invention may be employed for geochemical prospecting. In geochemical prospecting, earth samples are taken at spaced distances over the prospect area'either from the surface zones or the near-surface zones. Preferably, the earth samples should be taken at a distance of at. least one foot from the surface in order to obtain samples that have not been subject to weathering with consequent variation in their paraffin hydrocarbon content due'to causes other than the proximity or absence of a petroleum reservoir. The samples may be taken along a traverse or a plurality of traverses or otherwise over the prospect area in accordance with the usual procedures in the art. The earth samples are analyzed for the desired paraflin hydrocarbon and lipid content and the ratio of the amounts of parafiin hydrocarbon to lipids correlated with the respective sampling locations to detect possible anomalies indicative of a petroleum deposit.

The invention may also be employed in another geochemical exploration procedure, namely, well logging. The earth examples, comprising cores or cuttings, ob-

tained from successive levels as the drilling of the well proceeds are analyzed for the desired parafiin'hydrocarbon and lipid content and the ratio of the amounts of paraflin hydrocarbon to lipids are correlated with the locations in-the exploration zone, or the levels in the well, at which the earth samples were obtained to detect possible anomalies indicating proximity of a petroleum reservoir.

Analysis of the earth samples for the amounts of the desired parafiin hydrocarbon and the desired lipids may be made by-any suitable procedure. For example, the earth samples may be dried and crushed and then extracted with a suitable solvent to remove paraffin hydrocarbons and lipids as a first step in the analysis. .The lipids, as indicated hereinabove, as well as the paraflin hydrocarbons, are soluble inlany solvent capable of dissolving fats and accordingly any solvent capable of dissolvingfats may be employed for extracting the earth samples. Suitable solvents include carbon tetrachloride, chloroform, carbon disulfide, acetone, methanol, ethanol, propanol, 'diethyl ether, etc. Mixtures of solvents may also be employed such as an equimolar mixture of an alcohol and carbon tetrachloride. Paraflin hydrocarbon solvents. may also be used, provided, of course, that they will not be included among the paraffin hydrocarbons whose anomalies are being sought, that they may be removed from the extract prior to analysis, or that the method of analysis employed will distinguish between the desired paraffin hydrocarbons contained in the earth samples and those whose'presence is due to the solvent employed for extraction. Since the parafiin hydrocarbons and the lipids will constitute practically all of the material contained in the earth samples extractable by a solventcapable of dissolving fats, the amount of the paraflin hydrocarbons and the lipids may be determined by, removing all the solvent from the extract solution, as

by evaporation, and weighing the residue. Removal of the solvent by evaporation may be accomplished by any suitable procedure, but the temperatures. and pressures employed should be such as to avoid removal or destruction of any of the paraifin hydrocarbons having a boiling point higher than the boiling point of the solvent, if these parafiin hydrocarbons are to be included in the paraflin hydrocarbons for which analysis of the earth samples is to be made. While evaporation of the solvent from the solution of extract will remove parafiin hydrocarbons lower boiling than the solvent, the removal of these parafiin hydrocarbons, where the solvent is one ordinarily employed for extraction of earth samples, will not be significant with respect to the total quantity of paraffin hydrocarbons since, as well known in the art, unless particular precautions are taken in connection with the techniques employed for obtaining the earth samples, for extracting the earth samples, and for handling the solutions of extract, the light paraffin hydrocarbons will be lost to. the atmosphere. The amount of the parafiin hydrocarbons and the lipids may also be 7 determined with suflicient accuracy for the purposes of the invention by measurement of the extent of absorption of infrared radiation by the extract solution, as by measuring the extent of absorption by the extract solution of infrared radiation in the 3 to 4 micron range. By employing a procedure of this type, evaporation is avoided. Where an infrared absorption method is employed, of course, the extract must be contained in a solvent which is transparent to this infrared radiation.

Knowing the amount of the desired parafiin hydrocarbons plus the amount of lipids, the paraffin hydrocarbon-lipped ratio may be determined by measurement of the amount of either the desired parafiin hydrocarbons or the amount of the lipids. Any known procedure may be employed for separating the parafiin hydrocarbons from the lipids and measuring the amount of the paraffin hydrocarbons or measuring the amount of lipids. One method for separating the pa'raifin hydrocarbons and measuring their amount comprises saponification treatment of the mixture of paraffin hydrocarbons and lipids by addition thereto of a solution of metallic hydroxide, such as an alcoholic solution of potassium hydroxide, to convert the saponifiable lipids to soaps, removal of the unsaponifiable material, as by addition of salt such as sodium chloride followed by filtering, removal of excess salt, and treatment of the mixture with concentrated sulfuric acid at a temperature of about 100 C.

whereby all but the parafiin hydrocarbons are changed to water soluble or volatilized compounds. If. desired, the mixture prior to treatment with sulfuric acid may also be treated with acetic anhydride to remove any sterols which may not have been saponified and removed by the adding of salt and filtering. The mixture resulting from treatment with sulfuric acid is washed with water to remove water soluble material. The residue after drytion-fractionation while dissolved in a solvent which has a greater capability for being adsorbed on surfaces than the desired paraffin hydrocarbons but which has a lesser capability for being adsorbed on surfaces than the lipids. This procedure removes the lipids from the solution of extract, leaving therein all or part of the parafiin hydrocarbons, as desired. The amount of parafiin hydrocarbons can then be determined by removing the solvent from the extract solution and weighing, or determined by adsorption of infrared radiation. If desired, the lipids removed from the solution of extract may be recovered by desorption and their amount similarly determined.

Adsorption-fractionation comprises passing the paraffin hydrocarbons and the lipids in solution through a column of surface active material. By surface active material is meant any material which has a high surface area per volume of material. These materials are well ltnown in the art of chromatography and include si ica gel, alumina gel, clay, fullers earth, and other highly adsorbent materials. The more adsorbable constituents in the solution of extract are adsorbed first on the surface active material and, as the solution of extract percolates through the surface active material, the less adsorbable materials are progressively adsorbed. The solvent must be employed in amounts such that it will be the constituent in greatest volume in the solution of extract, i. e., ten. times as great as the total volume of the other constituents of the solution of extract, although larger volumes may be employed if necessary to insure sharper separation. The amount of surface active material to be employed must be sufficient to adsorb a part of the solvent and, co the lipids are more readily adsorbable than the parafiin hydrocarbons, the solvent leaving the column of su. 'ace active material will contain those constituents of the solution less adsorbable than the solvent. By selection of the solvent, part or all of the parafiin hydrocarbons will be the only constituents originally extracted from the earth sample leaving the surface active material in solution in the solvent.

in carrying out the adsorption-fractionation procedure, it is preferred to dissolve the extract containing the paraffin hydrocarbon and lipids in a small portion of the desired solvent and pour the relatively concentrated solution upon the top of the column of surface active marenal and thereafter pass the remainder of the desired volume through the column. The adsorption fractiona tion may also be carried out by placing the extract upon the top of the column of surface active material and thereafter pour the desired volume of desired solvent through the column.

The relative order of absorbability on surface active material, such as silica gel, of the classes of organic components ordinarily found in the earth samples and the ordinary classes of organic solvents in which paraffin hydrocarbons and lipids are soluble is as follows:

and saturated polycyclic In the above tabulation, the classes of compounds are listed in order of increasing adsorbability, i. e., the heavy isoparaffin hydrocarbons are less capable of being adsorbed on surface active material than the light isoparaffin hydrocarbons, the light isoparafiiu hydrocarbons are less capable of being adsorbed than the heavy normal parafiin hydrocarbons, etc.

The selection of the solvent for the extract solution to be passed through the column or" surface active ma erial may be made in accordance with the above tabulation. Thus, if the ratio of the heavy isoparaffin hydrocarbons as a group to the lipids is to be determined, light isoparafiin hydrocarbon solvent may be employed as the solvent for the extract during adsorption-fractionation. If the ratio of the heavy and light isoparaffin hydro carbons and the heavy normal paraffin hydrocarbons, as a group, to the lipids is to be determined, a light normal parafiin hydrocarbon may be employed as the solvent.

if; i)

Similarly, selection of the solvent may be made where the ratios of other parafiin hydrocarbons to the lipids are to be determined. For each solvent, those compounds preceding it in the above tabulation, and, where the solvent is a parafiin hydrocarbon, the heavier parafiin hydrocarbons within the same class, will be retained in the solution following adsorption-fractionation.

Generally, it is desirable to employ a solvent which is liquid at ordinary conditions of temperature and pressure. However, solvents which are solid or gaseous at ordinary conditions of temperature and pressure may be employed by maintaining proper conditions of temperature and pressure, or both, to keep the solvent in the liquid phase. Paraffin and isoparafiin solvents which may be employed for adsorption-fractionation include ethan v propane, normal butane, isobutane, normal pentane, isomeric pentanes, normal hexane, isomeric hexanes, normal heptane, isomeric heptanes, etc. Of these, normal pentane and normal heptane are preferred since each can retain, during adsorption-fractionation, all but a few of the light normal parafiins that may have been contained in the earth samples, each remains in the liquid state at ordinary temperatures and pressures, and when each is to be removed by evaporation, only a few of the light normal paraffins that may have been present in the solution will be removed along with the solvent.

Where the ratio of all the paraflin hydrocarbons as a group to the lipids is to be determined, halogenated solvents may be employed. With such solvents, of course, any naphthenes that may have been contained in the solution will not be removed by adsorption-fractionation. However, the amount of the naphthenes is usually very small as compared to the amount of the parafiin hydrocarbons and, therefore, can be neglected. Suitable halogenated solvents include carbon tetrachloride, carhon tetrabromide, carbon tetraiodide, and carbon tetrafluoride. These compounds have the advantage that quantitative determination of the parafiin hydrocarbon can be made following adsorption-fractionation by infrared absorption methods without necessity for removal of solvent by evaporation. Or" the halogenated solvents, carbon tetrachloride is preferred.

Solvents other than those mentioned above may be used and their suitability for use may be determined from knowledge of their adsorbabilities. The adsorbability of any solvent relative to paraffin hydrocarbons and the lipids may be measured by admixing the solvent with a small quantity of parafiin hydrocarbons or the lipids in the pure state, subjecting to adsorption fractionation in a column of surface active material, and analyzing the solution issuing from the column to determine whether the solvent or the earth sample constituent is preferentially adsorbed.

The solvent employed for extraction of the earth sample may be the same solvent to be employed in the adsportion-fractionation step, or may be a difierent solvent. Where a different solvent is employed, all the solvent is removed by evaporation from the solution obtained by extraction and the residue is subjected to adsorption-fractionation while dissolved in the dif lerent solvent.

If desired, the amount of paraffin hydrocarbons may be determined by desorbing the lipids from the column of surface active material, measuring the amount of lipids, and subtracting this amount from the total amount of parafiin hydrocarbon and lipids extracted from the earth sample. Further, by measuring both the amount of paraffin hydrocarbons obtained by adsorption-fractionation and the amount of lipids obtained by desorption, the ratio of the amount of paraffin hydrocarbons to lipids may be determined without the necessity of measuring the total amount of parafiin hydrocarbons and of lipids in the solution or" extract prior to adsorption-fractionation. For desorption of the lipids from the surface active material, any solvent more adsorbable than the lipids may be employed. Such solvents include the oxygenated compounds such as methanol, ethanol, propanol. etc. Following desorption, the amount of lipids in the solution may be measured by any suitable means, such as removal of the solvent by' evaporation and weighing the residue or by measurement of absorption of infrared radiation.

Knowing the amount of the parafiin hydrocarbons and the amount of the lipids, the ratio of the amount of paraffin hydrocarbons to the amount of lipids may be calculated for each sample. These ratios are then correlated With the sample locations in the exploration zone and anomalous ratios, i. e., ratios of the amount of paraffin hydrocarbon to the amount of lipids higher than the background ratios are regarded as indicative of the proximity of an underground petroleum reservoir. It is apparent, of course, that the ratios of the amount of paraffin hydrocarbon to the amount of lipids plus paraffin hydrocarbon may also be calculated from the amount of the paraflin hydrocarbon and the amount of the lipids and that these ratios will be equivalent to, and be within the purview of, the ratios of the amount of pitrafiin hydrocarbon to the amount of lipids with respect to being indicative of the proximity of an underground petroleum reservoir.

Herein, by extract I mean that portion of the earth sample, either prior or subsequent to adsorption-fractionation, which has been removed from the earth sample by extraction of the earth sample with a solvent and which may or may not be in solution. By solution of extract or extract solution I mean the extract in solution in a solvent, whether the solvent is one employed in extracting the earth sample, for carrying out adsorption-fractionation, or one in which quantitative determination of parafiin hydrocarbons as by infrared absorption is made. By residue 1 mean the extract as obtained by evaporation of its solution in any solvent. By parafiins I mean both normal paraffins and isoparafifins unless otherwise qualified.

The following example will be illustrative of the invention:

During the drilling of a well for oil, cores were taken at various depths as the drilling proceeded. A sample, weighing about 50 grams, was taken of each core, and after crushing and drying, was extracted with about 150 milliliters of a constant boiling mixture of methanol and carbon tetrachloride. the solution of extract at 40 C. with the aid of a stream of inert gas. The resulting residue'was extracted with successive 1O milliliter portions of carbon tetrachloride until substantially the entire amount of material soluble in carbon tetrachloride was removed therefrom. carbon tetrachloride was then removed from the solution of extract at 40 C. with the aid of a stream of inert gas and the residue, consisting of lipids and parafiin hydrocarbons, was weighed. The residue was next dissolved in 50 milliliters of normal heptane and subjected to adsorpnon-fractionation in a column of silica gel 10 centimeters in length and l centimeter in diameter. The silica gel was approximately 209 mesh in size and had been activated by heating at 425 C. for 6 hours. The normal heptane solution passing through the column of silica gel was evaporated similarly as the two previous solutions and the residue, consisting of paraffin hydrocarbons was then weighed. From the weight of the lipids and the weight of the paraffin hydrocarbons, the ratio of the amount of parafiin hydrocarbon to the amount of lipids for each sample was determined. The results, expressed as percentages, are given in the following table which also gives the depth at which the core was taken and the type of earth material constituting the core. 7

The solvents were removed from The Lat

Table 1 Ratio of Paraflin Hydrocarbons to Lipids Type of Earth it will be observed from the above table that the ratio of parafl'in hydrocarbons to lipids in the cores taken at 851 feet and below 1392 feet were appreciably higher than the ratio in the other cores. However, none of these cores, by visual or olfactory inspection, indicated the presence of oil. The formations at four different depths were subsequently acidized'. The table gives the depths of the formations and the results of the acidizing treatment.

Table II Depth, Feet Results Gas in commercial quantities and a small amount of 011 were produce 4 No productlon of gas or oil.

Gas and oil produced in commercial quantities.

It will be seen from Table II that the formations having high parafiin hydrocarbon-lipid ratios, i. e., 851 feet and 1,400 feet, produced commercial quantities of gas or gas and oil whereas the formations having low paraffin hydrocarbon-lipid ratios, i. e., 1,162 feet and 1,282 feet, produced neither gas nor oil.

This application is a'continuatiomin-part of my copending application, Serial -No.-85,252,' filed April 2, 1949, and now abandoned.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example only and not by way of limitation, reference for the latter purpose being had to the appended claims.

I claim:

1. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined paraffin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, quantitatively analyzing each of said earth samples for the ratio of the quantity of at least the same selected portion of the paraffin hydrocarbons contained in each earth sample to the in said ratios indicative of the proximity-of an underground petroleum reservoir.

2. ln a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the'content of predetermined'parafiin hydrocarbons and lipids contained in said earthsamples, the steps comprising collecting earth samples from 'saidexploration zone, quantitatively analyzing each of said earth samples for the amount of at least a selected portion of the parafiin hydrocarbons contained therein, quantitatively analyzing each of said earth samples for the amount of at least a selected portion of the lipids contained therein, the selected portion of the paraffin hydrocarbons and the selected portion of the lipids being the same for each of said earth samples, whereby the ratio of the amount of the selected portion of the paraffin hydrocarbons to the amount of the selected portion of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

3. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined paratfin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, quantitatively analyzing each of said earth samples for the amount of at least a selected portion of the paraiiin hydrocarbons contained therein, quantitatively analyzing each of said earth samples for the amount of the lipids contained therein, the selected portion of the paraffin hydrocarbons being the same for each of said earth samples, whereby the ratio of the amount of the selected portion of the parafiin hydrocarbons to the amount of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

4. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined parafiin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, extracting each of said earth samples with a solvent in which parafiin hydrocarbons and lipids contained in said earth samples are soluble to obtain an extract for each of said earth samples containing paralfin hydrocarbons and lipids contained in each of said earth samples, quantitatively analyzing each of said extracts for the amount of at least a selected portion of the paraffin hydrocarbons contained therein, quantitatively analyzing each of said extracts for the amount of at least a selected portion of the lipids contained therein, the selected portion of the paraffin hydrocarbons and the selected portion of the lipids being the same for each of said extracts, whereby the ratio of the amount of the selected portion of the paralfin hydrocarbons to the amount of the selected portion of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

5. in a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined parafiin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, extracting each of said earth samples with a solvent in which paraflin hydrocarbons and lipids contained in said earth samples are soluble to obtain a solution of extract for each of said earth samples containing parafiin hydrocarbons and lipids contained in each of said earth samples, the solvent being the (ill same for each of said earth samples, removing the solvent from each of said solutions of extract, quantitatively analyzing each of the resulting residues of the solutions of extract for the amount of at least a selected portion of the paraffin hydrocarbons contained therein, quantitatively analyzing each of the resulting residues for the amount of a selected portion of the lipids contained therein, the selected portion of the parafiin hydrocarbons and the selected portion of the lipids being the same for each of said resulting residues, whereby the ratio of the amount of the selected portion of the parafiin hydrocarbons to the amount of the selected portion of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with said sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

6. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined parafiin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth sampics from said exploration zone, extracting each of said earth samples with a solvent in which parafiin hydrocarbons and lipids contained in said earth samples are soluble to obtain a solution of extract for each of said earth samples containing paraffin hydrocarbons and lipids contained in each of said earth samples, the solvent being the same for each of said earth samples, removing the solvent from each of said solutions of extract, weighing each of the resulting residues of the solutions of extract to determine the amount or" the parafiin hydrocarbons and the amount of the lipids extracted from each of said earth samples, quantitatively analyzing each or" the resulting residues for the amount of the paraffin hydrocarbons contained therein, the parafiin hydrocarbons being the same for each of said residues, whereby the ratio of the amount of the paraffin hydrocarbons to the amount of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

7. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined parafin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, extracting each of said earth samples with a solvent in which paraffin hydrocarbons and lipids contained in said earth samples are soluble to obtain an extract for each of said earth samples containing parafiin hydrocarbons and lipids contained in each of said earth samples, quantitatively analyzing by absorption of infrared radiation each of said extracts for the amount of the parafiin hydrocarbons and the amount of the lipids extracted from each of said earth samples, removing lipids from each of said extracts, quan titatively analyzing each of said extracts for the amount of the paratfin hydrocarbons contained therein, the parafiin hydrocarbons being the same for each of said extracts, whereby the ratio of the amount of the parafiin hydrocarbons to the amount of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

8. In a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined paraffin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, quantitatively analyzing each of said earth samples under comparable conditions for the amount of at least a selected portion of the parafiin hydrocarbonscontained therein, quantitatively analyzing each of said earth samples under comparable conditions for the amount of at least a selected portion of the lipids contained therein, the selected'portion of the paraflin hydrocarbons and the selected portion of the lipids being the same for each of said earth samples, whereby the ratio of the amount of the selected portion of the parafiin hydrocarbons to the amount of the selected portion of lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

' 9. in a geochemical exploration method for determining the proximity of an underground petroleum reservoir in' which the proximity of such a reservoir to earth samples taken from predetermined locations in an. ex- 2 ploration zone is determined as a function of the content of predetermined paraffin hydrocarbons and lipids contained in said earth samples, the steps comprising collecting earth samples from said exploration zone, extracting each of said earth samples under comparable conditions with a solvent in which parafiin hydrocarbons and lipids contained in said earth samples are soluble to obtain an extract for each of said earth samples containing paraffin hydrocarbons and lipids contained in each of said earth samples, quantitatively analyzing each of said extracts under comparable conditions for the amount of at least a selected portion of the paraifin hydrocarbons contained therein, quantitatively analyzing each of said extracts under comparable-conditions for the amount of atleast a selected portion'of the lipids contained therein, the selected portion of the parafiin hydrocarbons and the selected portion of the lipids being the same for each of said extracts, whereby the ratio of the amount of the selected portion of the paraflin hydrocarbons to the amount of the selected portion ot' the lipids in each of the earth samples may be determined, and correlatingthese ratios for the various earth samples with the sample location'in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

'10. in a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined paraffin hydrocarbons and lipids containedin said earth samples, the steps comprising collecting earth samples from said exploration zone, extracting each of said earth'samples under comparable conditions'with a solvent in which paraflin hydrocarbons and lipids contained in said earth samples are soluble to obtain a solution of extract for each of said earth samples containing parafiin hydrocarbons and lipids contained in each of said earth samples, the solvent being the same for each of' said earth samples, removing the solvent from each of said solutions of extract, quantitatively analyzing each of the resulting residues of the solutions of extract under comparable conditions for the amount of at least a selected portion of the paraffin hydrocarbons contained therein, quantitatively analyzing each of the resulting residues of the solutions of extract under comparable conditions for the amount of a'selected portion of the lipids contained therein, the selected portion of the paraflin hydrocarbons and the selected portion of the lipids being the same for each of said resulting residues, whereby the ratio of the amount of the selected portion of the paraflin hydrocarbons to the amount of the selected portion of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir. V

ll. in a geochemical exploration method for determining the proximity of an underground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined locations in an exploration zone is determined as a function of the content of predetermined parafiin hydrocarbons and lipids contained in said earth samples, the steps comprisinglcollecting earth samples from said exploration zone, ex

each of the resulting residues of the solutions of extract t to determine the amount of the parafiin hydrocarbons and the amount of the lipids extracted from each of said earth samples, quantitatively analyzing each of the resulting residues of the solutions of extract under comparable conditions for the amount of the paratfin hydrocarbons contained therein, whereby the ratio of the amount of the parafiin hydrocarbons to the amount of the lipids in each of the earth samples-may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

12.'In a geochemical exploration method 'for determining the proximity of anvunderground petroleum reservoir in which the proximity of such a reservoir to earth samples taken from predetermined location'sfin an exploration zone is determined as a function of the content of predetermined par'aflin hydrocarbons and lipids contained in said earth samples, the steps comprising col lecting earth samples from said exploration zone,-extracting each of said earth samples under comparable conditions with a solvent in which parafiin hydrocarbons and lipids contained in said earth samples are soluble to obtain an extract for each of said earth samples containing parafiin hydrocarbons and lipids contained in each of said earth samples, quantitatively analyzing by absorption of infrared radiation each of said extracts for I the amount of the paratfin hydrocarbons and the amount of the lipids extracted from each of said earth samples, removing lipids from each of said extracts, quantitatively analyzing each of said extracts under comparable conditions for the amount of the paraflin hydrocarbons therein, whereby the ratio of the amount of the paraffin hydrocarbons to the amount of the lipids in each of the earth samples may be determined, and correlating these ratios for the various earth samples with the sample locations in said exploration zone to determine anomalous variations in said ratios indicative of the proximity of an underground petroleum reservoir.

References Cited in the file of this patent UNITED STATES PATENTS 2,320,577 Dunn June 1, 1943 2,336,612 Horvitz Dec. 14, 1943 2,343,772 Horvitz Mar. 7, 1944 

11. IN A GEOCHEMICAL EXPLORATION METHOD FOR DETERMINING THE PROXIMITY OF AN UNDERGROUND PETROLEUM RESERVIOR IN WHICH THE PROXIMITY OF SUCH A RESERVIOR TO EARTH SAMPLES TAKEN FROM PREDETERMINED LOCATIONS IN AN EXPLORATION ZONE IS DETERMINED AS A FUNCTION OF THE CONTENT OF PREDETERMINED PARAFFIN HYDROCARBONS AND LIPIDS CONTAINED IN SAID EARTH SAMPLES, THE STEPS COMPRISING COLLECTING EARTH SAMPLES FROM SAID EXPLORATION ZONE, EXTRACTING EACH OF SAID EARTH SAMPLES UNDER COMPARABLE CONDITIONS WITH A SOLVENT IN WHICH PARAFFIN HYDROCARBONS AND LIPIDS CONTAINED IN SAID EARTH SAMPLES ARE SOLUBLE TO OBTAIN A SOLUTION OF EXTRACT FOR EACH OF SAID EARTH SAMPLES CONTAINING PARAFFIN HYDROCARBONS AND LIPIDS CONTAINED IN EACH OF SAID EARTH SAMPLES, THE SOLVENT BEING THE SAME FOR EACH OF SAID EARTH SAMPLES, REMOVING THE SOLVENT FROM EACH OF SAID SOLUTIONS OF EXTRACT, WEIGHTING EACH OF THE RESULTING RESIDUES OF THE SOLUTIONS OF EXTRACT TO DETERMINE THE AMOUNT OF THE PARAFFIN HYDROCARBONS AND THE AMOUNT OF THE LIPIDS EXTRACTED FROM EACH OF SAID EARTH SAMPLES, QUANTITATIVELY ANALYZING EACH OF THE RESULTING RESIDUES OF THE SOLUTIONS OF EXTRACT UNDER COMPARABLE CONDITIONS FOR THE AMOUNT OF THE PARAFFIN HYDROCARBONS CONTAINED THEREIN, WHEREBY THE RATIO OF THE AMOUNT OF THE PARAFFIN HYDROCARBONS TO THE AMOUNT OF THE LIPIDS IN EACH OF THE EARTH SAMPLES MAY BE DETERMINED, AND CORRELATING THESE RATIOS FOR THE VARIOUS EARTH SAMPLES WITH THE SAMPLE LOCATIONS IN SAID EXPOLRATION ZONE TO DETERMINE ANOMALOUS VARIATIONS IN SAID RATIOS INDICATIVE OF PROXIMITY OF AN UNDERGROUND PETROLEUM RESERVIOR. 